Discover Scotland and Explore the Geodiversity and Fossils of Achanarras Quarry Near Caithness
- Wayne Munday
- 1 day ago
- 5 min read
Updated: 9 hours ago
Sip back and discover Scotland and explore the geodiversity and fossils of Achanarras Quarry located approximately 2 Km west of the village of Spittal in Caithness a Site of Special Scientific Interest (SSSI) and international geological significance telling a story of an ecosystem dating back to the Givetian Stage of the Middle Devonian epoch. The Achanarras Quarry opened in 1870 for extracting roofing tiles until 1961 and now presents a rare and significant exposure of the Achanarras Limestone Member a stratigraphic marker within the Orcadian Basin between the Upper and Lower Caithness Flagstone Groups recognised for its rich fossil fish assemblage that inhabited Lake Orcadie. This site is known for a wide range of fossil fish including Dipterus, Coccosteus, Pterichthyodes, Palaeospondylus, Mseacanthus, and small Diplacanthus. Scarcer species include Glyptolepis, Cheiracanthus, large Diplacanthus, Cheirolepis, Osteolepis, and Achanarella. Rare species such as Cornovichthys, Homosteus, and Rhamphodopsis have also been recorded contributing to the site’s global paleontological importance.
Achanarras Quarry is designated as a Site of Special Scientific Interest (SSSI) and managed by NatureScot. Fossil collecting at Achanarras Quarry is permitted but strictly regulated to ensure conservation and public safety. Collectors must adhere to the Scottish Fossil Code and obtain written permission from NatureScot to sell any specimens. For more information download the Guide to Ancharras Quarry Fossil Fish.
The site lies within the Orcadian Basin a vast inland depositional system that extended across present-day Shetland, Orkney and the Moray Firth during the Middle Devonian period approximately 398 - 385 million years ago. The fossil fish of Achanarras Quarry share similarities with the Sandwick Fish Bed located in the Sandwick area of Orkney exposed at Cruaday Hill Quarry. The Sandwick Fish Bed and Achanarras Fish Bed are closely related geological units within the Middle Devonian sequence of the Orcadian Basin in northern Scotland.
The Orcadian Basin was characterised by Lake Orcadie a large freshwater body of water that played a central role in shaping the sedimentary and fossil record of this northern region of Scotland. The geological formations at Achanarras Quarry chronicle important environmental changes that led to the deepening and shallowing of the lake during the Devonian Period. At the time, Scotland was located near the Equator and experienced a warm, dry climate with cyclical wet and dry periods.
The Achanarras Quarry is renowned for its exceptionally preserved fossil fish primarily found within the several meter thick Achanarras Limestone Member comprising primarily of calcareous flagstones and siltstones sandwiched in between the Upper Caithness Flagstone Group above and the Lower Caithness Flagstone Group below creating a well-defined geological sequence within the Old Red Sandstone in the Northern Highlands of Scotland.
Interestingly, the Achanarras Limestone Member exhibits layers of a fine lamination of alternating detrital quartz, carbonate and organic matter characteristic of an annual sedimentation regime consistent with a lake or lacustrine environment where seasonal cycles are driven by algal productivity and changing lake chemistry. The organic layers were formed from decaying algal blooms whilst the carbonate layers were deposited during periods of intense photosynthesis that increased water alkalinity. The fine clastic layers produced by the physical weathering of pre-existing minerals and rocks resulted from suspended sediment transported by seasonal rainfall and runoff. Together, these finely layered sediments offer valuable insight into the climate, hydrology and ecology of the Devonian Period in the Orcadian Basin.
Embedded within this limestone is the Achanarras Fish Bed a fossiliferous horizon deposited approximately 392 million years ago in Lake Orcadie during the Givetian Stage of the Middle Devonian epoch. The fish bed is well preserved likely resulting from periodic anoxic events within the lake that limited decomposition and scavenging. The fossil assemblage at the Achanarras Quarry includes at least sixteen well preserved species of Devonian fish making it the most prolific site of its age in Scotland and in Britain.
During the Devonian period, Earth’s aquatic ecosystems teemed with evolutionary innovation, giving rise to a rich diversity of early vertebrates that would shape the future of life on land and in the sea. The Achanarras Fish Bed includes over 18 species of fish from a number of diverse classes including the earliest jawed fishes the Acanthodii, or "spiny sharks." These slender, fin-spined pioneers are divided into two orders of Climatiformes, represented by the Diplacanthidae family and the Acanthodiformes, represented by the Acanthodidae. Species like Diplacanthus striatus, D. tenuistriatus, and D. (Rhadinacanthus) longispinus showcased streamlined forms ideal for swift movement, while Mesacanthus peachi and Cheiracanthus murchisoni featured more robust builds and prominent fin spines.
Alongside the agile spiny sharks swam the Placodermi, heavily armoured jawed fishes that dominated Devonian waters. The Antiarchi order included bottom-dwellers such as Pterichthyodes milleri, which boasted armoured, jointed pectoral fins likely used for locomotion along the seabed. In contrast, the Arthrodira, featuring powerful predators like Coccosteus cuspidatus and Homosteus milleri, exhibited movable head-armour and strong jaws suited for active hunting. Another branch, the Ptyctodontida, included softer-bodied species such as Rhamphodopsis threiplandi, which likely occupied a niche similar to modern rays, feeding on softer prey with specialised adaptations.
A major evolutionary leap came with the emergence of the Osteichthyes or bony fishes which would eventually give rise to all modern fish and land vertebrates tetrapods. This group split into two primary classes of the Actinopterygii (ray-finned fishes) and the Sarcopterygii (lobe-finned fishes). Early ray-finned fishes like Cheirolepis trailli displayed sleek forms adapted for agility while the lobe-finned sarcopterygians such as Glyptolepis paucidens and Osteolepis macrolepidotus developed fleshy, limb-like fins and internal skeletons hinting at the transition to land. Other lobe-finned groups like the Porolepiformes, including the robust Holoptychius species, were likely strong predators, while the Dipnoi, or lungfishes like Dipterus valenciennesi showed an early adaptation to life in low-oxygen environments with the evolution of primitive lungs.
Amid these classified lineages, the mysterious Palaeospondylus gunni stands apart. Small and enigmatic, its ambiguous features have eluded definitive classification though some scientists suspect it may represent a larval stage of a lungfish or a completely unique evolutionary path. For now, it remains incertae sedis where its place in the evolutionary tree still unresolved.
Two fossil fish species the Rhamphodopsis threiplandi Watson and Palaeospondylus gunni Traquair and the yielding of the first Scottish fossil record of Actinolepis, a noteworthy genus of fossil fish and a rare Chasmataspid an extinct arthropod related to modern horseshoe crabs have contributed towards making the Achanarras Quarry a reference point for Devonian vertebrate taxonomic, evolutionary palaeontology and diversification.
Visitors are reminded to follow the Scottish Outdoor Access Code and observe all safety precautions. Vehicles must be parked at the designated car park at the base of the track, and access to the quarry is on foot via a farm track. Visitors should leave gates as found and avoid disturbing livestock. Visitors can also enjoy a stone-built shelter and an interpretive trail linking the car park to the quarry enhancing the educational experience.
The quarry includes flooded areas and unstable slopes, marked with warning signs and fencing, which must be avoided. Due to the site’s rugged and exposed nature, visitors are advised to wear warm, waterproof clothing and durable footwear, preferably with steel toecaps.
